A method and authenticator for authenticating a device in a system using the electrical properties of the device is disclosed. Embodiments of the disclosure enable authentication by receiving a plurality of input seed values from a requestor. For each input seed value, load stimuli are generated to produce an electrical load sequence on a power delivery network powering at least part of the system. Noise induced in the power delivery network is measured in response to the electrical load sequence using one or more sensors located on the power delivery network. Based on the measured noise, a dynamic response property (magnitude and phase response as a function of frequency) of the power delivery network corresponding to a respective input seed value can be determined and returned to the requestor.